The present invention relates to an active matrix panel having a light shield film around pixel electrodes, which is applied to liquid crystal display devices of active matrix type and the like.
FIGS. 10 and 11 show a part of an active matrix panel which has been applied to a conventional liquid crystal display device of active matrix type. FIG. 10 is a top view with a semiconductor thin film 8 and a channel protection film 9 shown in FIG. 11 omitted. This active matrix panel has such a structure that gate lines (scanning lines) 2 and drain lines (signal lines) 3 are disposed in a matrix form, and a thin film transistor 4 and a pixel electrode 5 are disposed near each intersection.
In predetermined locations of the top surface of a glass substrate 1, gate lines 2 including gate electrodes 6 are formed. Over the entire top surface thereof, a gate insulating film 7 is formed. In predetermined locations of the top surface of the gate insulating film 7, semiconductor thin films 8 made of amorphous silicon, poly-silicon, or the like are formed. In the central part of the top surface of each semiconductor thin film 8, a channel protection film 9 is formed. On both sides of the top surface of each semiconductor thin film 8, a drain electrode 10 and a source electrode 11 are formed. Simultaneously with the forming of the electrodes 10 and 11, drain lines 3 are formed. In each of predetermined locations of the top surface of the gate insulating film 7, a pixel electrode 5 made of ITO is formed so as to be electrically connected to one of the source electrodes 11. In FIG. 10, a chain line represents an opening 12 of a black matrix formed in a common electrode panel (not illustrated) having a common electrode (not illustrated). The common electrode panel and an active matrix panel are stuck together at their peripheries by a seal member inserted therebetween. A space between the common electrode panel and the active matrix panel is filled with a liquid crystal material. Corresponding to a voltage applied between the pixel electrode and the common electrode, the light transmission factor of the liquid crystal material changes to conduct a display. In the case of a color liquid crystal display device, color filter elements are arranged in the opening 12 of the common electrode panel.
In such a conventional active matrix panel, a clearance C.sub.1 of some degree is formed between the gate line 2 and the pixel electrode 5 and between the drain line 3 and the pixel electrode 5 in order to prevent the voltage to be applied to the pixel electrode at the time of driving from being largely affected by the gate signal and drain signal (partly in order to reduce the parasitic capacitance generated between the gate line 2 and the pixel electrode 5 and between the drain line 3 and the pixel electrode 5) and in order to prevent a short circuit between the drain line 3 and the pixel electrode 5. This clearance C.sub.1 is an area having no pixel electrodes 5. Since the clearance C.sub.1 always transmits (or intercepts) light, it must be covered by a light shield film. Furthermore, in order to prevent the characteristics of the thin film transistor 4 from being changed by exposure to external light, it is necessary to intercept light for the area corresponding to the thin film transistor 4 as well.
As shown in FIG. 10, therefore, the light shield film has a pattern in which the openings 12 are arranged in a matrix form. In general, the light shield film is called black matrix.
In the case where the clearance C.sub.1 and the thin film transistor 4 are to be covered with the light shield film, a clearance C.sub.2 of some degree is provided between edges of the opening 12 and the pixel electrode 5 of the black matrix in due consideration of misalignment caused when the active matrix panel and the common electrode panel are stuck together. Therefore, the size of the opening 12 of the black matrix must be made smaller than the size of the area surrounded by the gate lines 2 and the drain lines 3 by at least the sum value of the clearances C.sub.1 and C.sub.2. This results in a problem of reduced opening factor. The misalignment in sticking together the active matrix panel and the common electrode panel is typically 5 to 6 .mu.m. Therefore, the opening factor of liquid crystal display devices is nothing but approximately 50%.